1. Field of the Invention
This invention relates to a surface treatment for plasticized polyvinyl chloride substrates, and particularly to a method for coating such substrates so as to prevent plasticizer migration from the substrate to the topmost layer coating the substrate.
2. Description of the Prior Art
The surface of plasticized polyvinyl chloride often becomes tacky as a result of plasticizer migration from the interior of the vinyl composition. In an effort to prevent or inhibit such migration, it has been the preferred technique to coat such substrates with various polymeric materials. Among the most popular polymeric coatings for plasticized PVC substrates are the acrylic ester polymers, polyvinyl acetate, modified polyamides or polyurethanes. U.S. Pat. No. 3,669,717 discloses that plasticized polyvinyl chloride surfaces can be prevented from becoming tacky by coating such with a poly-gamma-alkyl glutamate held to the polyvinyl chloride surface by a primer coating of homopolymer or copolymer of PVC having a low degree of polymerization (500 or less). However, the coatings of this invention cannot be used on flooring materials because of the poor traffic abrasion properties. While the remainder of the above polymers are somewhat effective for the purpose for which they are intended, they also are not entirely satisfactory from the standpoint of inadequate resistance to wear and solvents. Of particular concern is the fact that the most satisfactory of the wear-resistant polymers, the polyurethanes, when used over plasticized polyvinyl chloride substrates do not actually prevent plasticizer migration, but in fact, become themselves plasticized, leading to a diminution of wear resistance and undesirable traffic staining.
It has now been found that multiple coatings over plasticized polyvinyl chloride substrates can significantly retard the diffusion of plasticizer to the surface of the coated article.